The invention relates to an electromagnetic actuator, especially for the closure member of a valve, having a solenoid unit, which has a cylindrical cavity closed at one end and open at the other end in which an axially introduced guide tube for a magnetically movable armature is arrestable by means of a securing device engageable in a first recess under spring force.
An actuator of that kind is known from U.S. Pat. No. 4,683,453. With this actuator, the securing device is a forked sheet-metal spring having two limbs that have hooks at their free ends. After the guide tube has been introduced into the cavity, the securing device has to be introduced from the outside, through a slot extending radially through the wall of the solenoid unit, into an annular groove, forming the first recess, on the circumference of a collar of the guide tube; for removal of the guide tube from the cavity, the securing device has to be pulled partially out of the slot. Both in its inserted position and in its pulled-out position the securing device protrudes inconveniently beyond the circumference of the solenoid unit because of an angled handle, so that a user may sustain injury when handling the actuator. Furthermore, introduction and pulling out of the guide tube requires manipulation of the securing device each time.
In the case of similar actuators (U.S. Pat. No. 4,055,823=DT 25 22 677 B2, U.S. Pat. Nos. 5,581,222, 4,805,870, 3,917,218, 3,727,160, WO 96/12906) the securing device also lies partially or wholly outside the solenoid unit, and in the case of some of these actuators can be removed completely, either intentionally or unintentionally. Furthermore, in some of these known actuators, the guide tube projects with both ends from the solenoid unit, so that the cavity can more easily become contaminated.
The invention is based on the problem of providing an actuator of the kind mentioned in the introduction, in which the connection between the solenoid unit and the guide tube is simpler and safer both to produce and, in case of need, to release, but which actuator is nevertheless simpler to manufacture.
That problem is solved in accordance with the invention in that the securing device lies completely within the solenoid unit and automatically snaps into the first recess when the guide tube is moved into a desired position in the cavity of the solenoid unit.
In particular, the securing device can be mounted in a second recess formed in the inner side of the wall of the cavity and can be arranged to be pressed laterally out of the cavity by a relative movement of the guide tube and the solenoid unit.
In this construction, connection and separation of the solenoid unit and the guide tube is possible merely by respectively fitting together and pulling apart these two parts, without the securing device having to be manipulated additionally. Further, fitting together can be rendered automatic in a simple manner. Since the securing device lies in each position inside the magnetizing coil, the risk of injury to the user of the actuator by the securing device is avoided. The securing device can be of a very simple form without a handle and hooks, so that it can be manufactured easily using little material.
Preferably, provision is made for the first recess to be formed in a magnet core, and for the magnet core to be connected to an end portion of the guide tube introduced into the cavity. The magnet core increases the strength of the magnetic flux within the cavity and hence the relative force of attraction of solenoid unit and armature, that is the operating force of the actuator, for the same number of ampere-turns of the magnetizing coil. The first recess can be formed in a simple manner with largely oblique lateral surfaces, which, firstly, facilitate introduction of the guide tube through the axial force component exerted over one oblique lateral surface as the securing device snaps in and, secondly, facilitate lateral pushing away of the securing device out of the cavity into the second recess over the other oblique lateral surface. In this case, the securing device at the same time additionally takes on the function of securing the installed position of the magnet core. Additional means for securing the position of the magnet core are consequently unnecessary. The magnetic core is mounted at the same time as the guide tube.
A development of the invention can consist in that the second recess is formed in the inner side of a coil former, which inner side bounds the cavity, and at the same time in an end face of the coil former, the coil former being surrounded by the magnetizing coil, and is covered by a magnet yoke lying adjacent to this end face. This development enables the second recess to be formed in a simple manner, since the end face of the coil former is initially readily accessible. After that, the recess can be bounded and hence completed by the abutting lateral surface of the magnet yoke covering it, the magnet yoke also increasing the strength of the magnetic flux and hence the relative force of attraction of solenoid unit and armature for the same number of ampere-turns of the magnetizing coil.
The magnet core can be introduced into an opening in the magnet yoke. This avoids a relatively large air gap between magnet core and magnet yoke.
The first recess is preferably an annular groove. The annular groove facilitates connection of the solenoid unit and guide tube, since no attention need be paid to maintaining a predetermined rotated angular position of the guide tube relative to the securing device as the guide tube is introduced into the cavity.
The securing device is preferably a spring wire, which is engageable with a portion of its length in the first recess. Such a spring wire is a very simple component that is easy to manufacture. For mounting, the spring wire merely needs to be inserted with its ends into the ends of the recess. Its middle portion is then flexible for the largest part of the length of the second recess.
In particular, this can be achieved in that the second recess extends along a plane intersecting the guide tube parallel to its longitudinal axis, and extends transversely to the longitudinal direction of the guide tube, is, over the largest part of its length perpendicular to the plane, deeper than the spring wire is thick, and at its ends perpendicular to the plane has a depth corresponding to the diameter of the spring wire.
Alternatively, the securing device can be a spring-loaded ball or a clip having two flexible arms.
The magnetizing coil, the coil former, and the magnet yoke are preferably embedded in plastics material. This fixes these components relative to one another. At the same time, the cavity is sealed at its one end.